The present invention relates generally to radiological well logging methods and apparatus for investigating subsurface earth formations traversed by a borehole and, more particularly, to a method and an apparatus for identifying and measuring the element vanadium in subsurface formations.
It is known that crude oil contains minute amounts of a wide variety of miscellaneous substances, some organic and some inorganic. Several elements that have been identified in crude oil ash include silicon, iron, aluminum, lead, tin, nickel and vanadium. Most of these elements are found in sea water and may have been derived from it, either as compounds in colloidal suspension or as materials secreted by algae or other marine organisms, which may also have provided the material from which petroleum was formed. It is known that vanadium and nickel are concentrated in the porphyrins and replace the magnesium in chlorophyll, with the results that the vanadium and nickel content of crude oil is frequently several thousand times greater than the concentration in the earth's crust. Vanadium can be present in crude oils in the range of concentrations from between 0 to 6,000 ppm.
The making of a quantitative measurement of the vanadium content in crude oils is useful for several reasons. The combustion characteristics of vanadium in residual oil may contibute to the deterioration of furnace linings and to the corrosion of boiler tubes or gas turbine blades. Catalyst poisoning by vanadium in refining processes may result in the formation of higher percentages of coke and gases at the expense of more desirable liquid products. Additionally, physical properties of crude oils, such as viscosity and flow rate, are related to vanadium content. For example, the viscosity of certain heavy crude oils is directly related to the concentration of vanadium. A good measurement of viscosity in heavy crude allows an optimal well stimulation technique, such as flooding, to be chosen to provide the most complete hydrocarbon recovery.
Accordingly, the present invention provides method and apparatus for identifying and measuring the element vanadium in-situ by radiological well logging.